Conventionally, the flight controls of an aircraft include a control stick.
The control stick is then connected to flight control members of the aircraft via a control line that may be mechanical, or electrical in modern aircraft. By moving the control stick from front to back and from left to right, the pilot can control the aircraft being piloted.
More particularly, a helicopter has a main lift and propulsion rotor that has a plurality of blades.
By adjusting collectively and identically the pitch of the blades, the pilot varies the magnitude of the overall lift of the main rotor so as to control the altitude and the speed of the helicopter. The pilot performs this action with the help of a collective flight control implementing a pitch lever that is commonly referred to as the “collective pitch lever”.
In contrast, by controlling the cyclical variation of the pitch of the blades with the cyclical flight control stick, which stick is referred to below as the “control stick”, the pilot controls the attitude of the aircraft and its movement in translation.
As a result, helicopters are generally provided with a swash plate comprising a rotary plate and a non-rotary plate. The rotary plate is connected to the blade via pitch levers, while the non-rotary blade is connected to servo-controls that are themselves controlled by the pilot's flight controls via electrical or mechanical transmission means.
By moving the control stick from front to back, the helicopter pilot controls in pitching the helicopter. And likewise, by moving the control stick from left to right, the pilot controls the roll of the helicopter.
It can be understood that the controls need to be precise in order to avoid leading to incidents.
Unfortunately, with certain prior flight controls, coupling is observed to appear between the pitch and roll controls. Specifically, by moving the control stick forwards, for example, it is found that the pilot modifies both pitch and roll simultaneously as a result of the dynamics of the control stick.
Document EP 0 522 623 discloses a flight control provided with a pitch and roll control stick suitable for avoiding the above-specified coupling phenomenon.
The bottom end of the control stick is hinged to a support that is fastened to the floor of the aircraft. In addition, a roll control rod is hinged to a projection secured to said bottom end.
Furthermore, a pitch control rod is mechanically connected to an intermediate segment of the control stick via first and second cranks.
More precisely, the pitch control line comprises in succession: the control stick, the first crank, the second crank, and then the pitch control rod.
The device described in that document EP 0 522 623 suggests isolating the pitch and roll controls in order to solve the problem.
Nevertheless, it is found that the device is bulky, with the pilot facing different flight control members.